PROJECT SUMMARY Optical coherence tomography (OCT) is a cross-sectional and 3-dimensional (3-D) imaging technology with very fine spatial resolution (5 ?m). This project develops the methods and software needed for high-precision OCT measurements of the eye to guide implant, laser, and transplant surgeries in the front part of the eye. In the proposed continuation of the project, a new generation of OCT that has very high speed (about 10 times faster than before, taking an image in as little as 2/1000 of a second) and extended range will enable new types of measurements to be done accurately. The Specific Aims are as follows: (1) To develop ultrahigh-speed OCT hardware and software for measuring optical surfaces of the anterior eye. Intrinsic eye movements effectively limit measurement of corneal shape by commercial OCT. This will be overcome by several approaches, including ultrahigh-speed OCT at 500 kHz, dual-beam OCT to simultaneously capture the shape of both the cornea and lens, simultaneous capture of Placido-ring videokeratography, and motion correction software. The goal is to provide reliable measurements on front and back surfaces of both the cornea and crystalline lens. (2) To develop an OCT-based intraocular lens power formula. Currently, surgeons lack an accurate way to calculate precise intraocular lens (IOL) power for cataract patients who previously had laser vision correction. These patients may be left near- or far-sighted after cataract surgery. An OCT-based IOL formula, using measurements of both anterior and posterior corneal powers, can give surgeons more precise information that will significantly improve visual outcomes. The OCT-based IOL formula will be tested in a clinical trial. (3) To develop OCT-guided excimer laser surface ablation. The excimer laser can remove cloudy layers from the front of the cornea and correct distorted shape due to keratoconus or transplant surgery. We have developed 3-D OCT-based planning to optimally remove cloudiness due to corneal scars and stromal dystrophies. This method will be tested in a larger clinical trial. We will improve the method by adding 3-D OCT measurement of corneal shape (topography) to plan the correction of any shape distortion. (4) To develop OCT-guided laser-assisted anterior and posterior lamellar keratoplasty. Most corneal diseases involve only the inner or outer layer of the cornea. Thus a partial thickness transplant can treat these diseases while avoiding the complications of full-thickness transplantations (rejection, irregular wound shape, etc). However, manual dissection of corneal layers is technically difficult and vision after surgery is limited by the rough interfaces. We have developed OCT methods to guide the shaping and smoothing of donor and host corneas with a combination of excimer laser to create smooth interfaces and femtosecond laser to create tongue-in-groove edge fits. Pilot clinical trials of these techniques are proposed. The goal is to develop surgeries that reliably improve the vision in patients with keratoconus, corneal dystrophies, and deep scars.